[vettestr]

No higher octane fuel will not help and maybe a bit worse depending on what they are testing. Have you tweeked it to get closer? Is it an idle only test or the loaded testing?
On a carb engine adjust idle ratio to lean miss and increase a tiny bit above miss, increase initial timing about 7 degrees if not already in the 15+ range for static timing.
Get engine up to operating range and mist a water fog into carb to remove any carbon build up = hold running engine at 2000 RPM and squirt a mist of water into carb throat, do this for about 5 to 8 pumps of the water bottle and then allow to return to idle. ( the water bottle is type a fog or fine mist comes out of the spray nozzle= like your mother used to iron clothes with) if you are older than them new fangled steam irons anyway ..... The cold water mist enters the combustion chamber and breakes loose the carbon build up. Be safe during all this and maybe get a helper to assist.